In most optical scanners, generally, a rotating mirror is used to deflect an incident beam of light. The rotation may be continuous, as in multifaceted polygons, or vibrational, as in galvanometers and piezoelectric deflectors. The light beam rotates proportional to the rotation of the facet and is focused along its path, to a flying spot, which sweeps along a line on a surface. The resolution of the system is directly proportional to the width and angular rotation of the reflecting mirror. To obtain a higher resolution between two successive spots along the scan line, and to avoid vignetting of the reflected light beam during scanning, a wider facet with a larger angular rotation is required. On the other hand, to achieve a higher scanning speed in a more compact design, a smaller facet with smaller angular rotation must be used. These two opposing requirements, impose a rather tight limitation on the speed and resolution of the optical scanners. For example, in most practical underfilled polygon scanners used in laser printers, the number of facets is 8-14, the polygon diameter is 75-80 mm, the facet width is 18-25 mm, and the angle subtending each facet is 25-45 degrees. A natural way to increase the scanning speed is to increase the number of facets, but this will decrease the field angle and scan length proportionally and the resolution by a power of 2. Overfilled polygon scanners permit a smaller polygon with a larger number of facets, but due to the truncation of the reflected light, the spot is not circular, spot light intensity is variable, and most of the light energy is wasted (see U.S. Pat. No. 3,995,110). Facet tracking in overfilled systems reduces these difficulties, but it adds to the complexity and price of the device (see U.S. Pat. No. 4,205,348). Also, there is the drawback of smaller scan field angle and larger focal length. Presently, in the state of the art high speed and ultra high speed scanners and printers, and general trend is to use high speed polygons. For example, in Hitachi printer, model DIPS-6000, the polygon rotates at 42000 rpm. However, high speed rotation introduces many problems such as critical manufacturing specifications, polygon dynamic instability, excessive distortion of the facets, siren noise, excessive wear, and higher stress.
Therefore, it is desirable to have a system that satisfies all requirements, while working at a lower rotational speed.